An intensive sheep production system using flocks of 100 Scottish Halfbred (SHB), 100 Welsh Speckleface (WSF) and 100 Finn Blackface (FBF) ewes maintained by 8, 4 and 6 ha grassland respectively for a 5-year period, was investigated to establish the consequences of high flock prolificacy and the measures taken to achieve it, including PMS administration. Mating occurred in late October/November at ewe: ram ratios of 25 or 33: 1. Ewes were housed in winter and fed silage, with supplementary cereals in late pregnancy. Lambs in excess of 2 (SHB) and 1 (WSF and FBF) per ewe were artificially reared and fattened indoors; ewes and lambs at grass were rotationally grazed (with forward creep grazing by the lambs). Prolificacy in the SHB breed was 225 lambs born per 100 ewes mated for untreated ewes and 237 for hormone-treated ewes; 119 and 155 respectively for WSF ewes; and 255 for FBF ewes (all untreated). Lambs sold per 100 ewes mated were: for SHB, 200 and 177; WSF, 102 and 107; FBF, 201.

Good ewe condition and heavy live weights at mating were associated with appetite problems on silage in late pregnancy; PMS injection with a failure to secure conception rates above 80% at the critical oestrus and a markedly lower prolificacy for ewes conceiving at later oestruses; mating in the middle of the breeding season and March/April lambing with slow lamb growth rates on grass in July and August. Hormone-induced high prolificacy was associated with a greater proportion of large multiple litters than natural high prolificacy, and consequent smaller lamb birth weights and more perinatal mortality. There was a significant negative regression relating fleece weight with litter size. The results suggest the existence of an optimal level of prolificacy for the system employed.

1. A total of 33 energy balance trials was conducted with veal calves offered a high-fat milk replacer diet containing 10, 20, 40 or 100 mg iron/kg DM.

2. There were no significant differences in weight gain, food conversion or energy retention between calves receiving 20, 40 or 100 mg iron/kg DM in their diet. Calves receiving only 10 mg iron/kg gained weight and retained energy at significantly lower rates than those in the other groups.

3. The metabolic heat production of calves receiving the liquid diet was greater than that of calves given the same amount of gross energy from a barley diet. The recommended air temperature of about 20°C for veal calf houses is therefore unnecessarily high.

In two experiments carried out in the autumn of 1971 and 1972 (treatment prefixes 1 and 2 respectively), 84 Finn x Dorset ewes found by X-ray to carry from 1 to 4 foetuses were individually fed during the last 6 weeks of gestation either: 1A, ad libitum; 1H and 2H, 33 kcal M/kg ewe live weight+365 kcal per ME/kg foetus (anticipated birth weight); 1M, 80%; and 2L, 50% of the total energy fed to treatments 1H and 2H. The amounts given remained constant during the experimental period. The method of feeding according to foetal number within treatments, attempted to standardize the nutritional state within treatments.

All ewes (except those on 2L which remained constant) gained 6 to 8 kg live weight during the last 6 weeks of gestation and lost 8 to 10 kg at parturition. The birth weight of lambs was not affected by the range of energy (2·3 to 4·4 Meal ME/ewe per day) consumed during the last 6 weeks of gestation.

Plasma concentrations of free fatty acids (FFA), glucose and ketone bodies were determined weekly. The mean FFA levels were significantly higher in the low energy treatment groups than the high ones.

The present data indicated that if there is little change in body weight i n the early stages of pregnancy a 65 kg ewe bearing twin lambs, will require about 4 Meal ME/day during the last 50 days of gestation t o prevent a rise in plasma FFA concentration or loss of weight over the gestation period.

The value of E, defined as the weight of carcass produced per 100 units of digestible organic matter (DOM) consumed, was used to assess the biological efficiency of meat production in housed sheep. The effect on E of weaning lambs at 4, 6, 8, 10, 12, 14 and 16 weeks post partum was studied for a number of different breed crosses. The age at which lambs were weaned was found to have little effect on the growth rate of lambs and no significant effect on the biological efficiency with which sheep produce meat.

1. Weanling male rats were used in three experiments to evaluate the sequence of limiting amino acids for maximum growth with diets based on wheats containing 10, 13 or 17% crude protein (N×5·71).

2. Lysine was the first-limiting, threonine the second-limiting, and valine or methionine the third- or fourth-limiting amino acid for growth rate and feed-conversion ratio of rats offered the diet based on wheat containing 10% crude protein. A further four amino acids (isoleucine, histidine, tryptophan and tyrosine) were limiting for feed-conversion ratio only.

3. For the diet based on wheat containing 13% crude protein the sequence of limiting amino acids was lysine, threonine and methionine.

4. Only lysine was limiting in the diet based on wheat containing 17% crude protein.

5. Plasma-free amino-acid concentrations were found to be a valuable criterion for prediction of the first-limiting amino acid in diets.

6. Improvement of growth and feed-conversion ratio was observed with diets based on wheat containing 17 or 13% crude protein when the limiting amino acids were supplemented to provide the recommended allowance. Further improvement in feed-conversion ratio was obtained when lysine and threonine were provided in excess of the recommended allowances.

7. There was a lysine-threonine interaction affecting growth rate and feed-conversion ratio, and a lysine-me.thionine interaction affecting feed-conversion ratio.

Forty litters were weaned from their Landrace × Landrace × Large White dams at 2-day intervals to give a range of lactation lengths from 4 to 42 days. A significant (P<0·001) negative curvilinear relationship was observed between lactation length and the interval from weaning to first oestrus. This period was increased by 4·2 days with the reduction of lactation from 42 to 4 days. The relationship between lactation length and the interval from farrowing to remating was significant (P<0·001) and positively linear over the whole range of observations. A decrease of 1 day in lactation length reduced this interval by 0·91 days. Very short lactations were associated with reduced litter size at the following farrowing; sows weaned after lactation lengths between 4 and 21 days had an average litter size of 9–6 piglets born per litter in the next parity, whereas sows weaned following lactation lengths between 21 and 42 days had an average of 12·7 piglets born in the next parity (P<0·01).

By fitting a range of numerical values to a model, genetic responses from performance testing male pigs (boars) were examined in a population in which pig farms either conduct their own tests or send boars to a central station for testing. Where selection intensities are the same for station and farm tests the former almost always has an advantage over the latter. Factors which lead to this advantage are genetic differences between farms, genetic sampling within farms and limitations on the accuracy of performance measurement in farm tests. In a large station test response in a trait of 50% heritability is expected to be 15% greater than in tests comprising boars from 10 effective parents on farms whose average genotype contributes 5% of the total genetic variation and whose environmental variation is 25% greater than in the station. In populations with limited station testing space available, farm tests should be able to compensate for their lower efficiency by increasing selection intensities.

An experiment was conducted using 176 sows at three centres to investigate the effect of post-weaning feed level on reproductive performance. At two centres sows weaned 35 to 56 days after farrowing received 1·8, 2·3, 3·6 or 4·5 kg food/day from the day following weaning until the day following the last mating at the post-weaning oestrus.

At the third centre sows were rationed to 1·8, 2·3 or 3·6 kg food/day or given all they would consume in a single 1-hr feeding period each day. Reproductive performance of the sows was not significantly affected by post-weaning feed level.

Data from 726 male and 765 female pigs (364 litters) from 28 threebreed crosses obtained from mating Poland China boars to gilts and sows from different two-breed-crosses were analysed. The 28 two-breed-crosses were obtained from mating Yorkshire (Y), Landrace (Ld), Lacombe (Lc), Hampshire (H), Duroc (D), Berkshire (B) and Large Black (LB) sows to Ld, Lc, H, D, B, LB and Tamworth (T) boars in an incomplete diallel mating design. The traits studied were age at slaughter (72 kg carcass weight), carcass backfat measurement and an index combining both traits.

The youngest pigs to reach slaughter weight were those from LB x D sows (191·3 days) while the oldest were from T x D sows (211·6 days). The pigs with the least depth of backfat were those involving the Hampshire breed (mean 7·28 cm) while those involving the Large Black had the thickest backfat (mean 7·81 cm). In descending order, the five highest ranking crosses based on the index were those from H x Ld, H x Lc, LB x D, Lc x Ld and H x Y sows.

An experiment was conducted with 60 male Friesian calves between 5 and 11 weeks of age. The experiment was a 5×2×2 factorial design. The five major treatments were the inclusion of 20 or 40% ground wheat straw or 20, 40 or 60% ground lucerne in a pelleted diet. A methane inhibitor was included in the diet given to 30 of the calves. The diets were given alone or with a chaffed wheat straw supplement ad libitum. All diets contained 2% sodium bicarbonate.

The weight gain of the calves was greater with the diets containing ground lucerne than with those containing ground wheat straw, but in both cases weight gains were reduced with increasing roughage content of the diets. The efficiency of feed conversion showed a similar trend. The supplementation of the diets with chaffed wheat straw did not affect the performance of the calves. The inclusion of the methane inhibitor in the diets improved the weight gains and efficiency of feed conversion. The daily retention of nitrogen in the calves showed a similar trend to the growth rates.

The molar percentage of acetate in the rumen increased as the roughage content of the diets increased while the proportions of propionate, butyrate and valerate decreased. The inclusion of the methane inhibitor in the diets decreased the concentration of total volatile fatty acids (VFA) in the rumen and increased the molar percentage of propionate, butyrate and valerate.

The growth performance, carcass quality and digestive efficiency of growing pigs were used to compare sweet lupin seed meal (SLSM) to soya bean meal and meat meal as a source of supplementary protein to wheat in diets for pigs, and to study the influence of low levels of lysine and methionine, high levels of crude fibre and oil, and possible toxic factors in SLSM on the use of SLSM in such diets.

The growth rate and food utilization of pigs between 20 and 80 kg live weight were in the order soya bean meal > SLSM > meat meal, but only the difference between soya bean meal and meat meal was significant. These feeds did not differ significantly in their effects on the proportion of lean in the ham. Adding lysine to the SLSM diet improved growth performance but adding methionine did not. The digestibility of crude fibre in diets containing SLSM was greater than that in diets containing soya bean meal; the digestible energy contents of SLSM and soya bean meal were 4·13±0·05 and 4·16±0·08 Mcal/kg dry matter, respectively. Pigs fed on a diet containing 27·5% SLSM grew faster but utilized food as efficiently when fed ad libitum as on a restricted scale of feeding. The subcutaneous fat of pigs fed on SLSM had a higher iodine number than that of pigs fed on soya bean meal.

The live-weight changes of 48 sows were recorded over three reproductive cycles. All sows were given standard amounts of feed in gestation and one of four energy allowances during lactation. The daily intakes of digestible energy during lactation ranged from 12·2 to 182·2 Meal in the first, 122·9 to 192·6 Meal in the second and 132·2 to 202·2 Meal in the third lactation. Weight change in lactation responded to energy intake; sows on the lowest energy intake lost weight whilst those on the highest intake gained. At weaning of their third litters, sows on the highest energy allowance weighed 44 kg more than those on the lowest level and this was equivalent to a carcass difference of 372·3 kg at slaughter.

All the sows were slaughtered after the third litters had been weaned and the carcasses were dissected into lean, subcutaneous fat+skin, and bone. Sows from all treatments had less subcutaneous fat+skin and more muscle and bone than non-pregnant gilts killed at a mean weight of 129 kg, a weight equivalent to that of the experimental animals at their first mating.

The reduction in fat reserves was linearly correlated with dietary energy intake of the sows. Sows receiving the lowest energy intake in lactation possessed fat reserves which were estimated to be only 25% as great as in gilts comparable to those used to initiate the experiment. This reduction in body reserves has implications with regard to the long-term effects of feeding lactating sows low intakes of energy during 6-week lactations.

1. Pelleted grass and a concentrate containing 90% rolled barley and 10% soya bean meal were offered to cows in three combinations, 25: 75, 50: 50 and 75: 25 respectively, together with a constant low level of coarse roughage.

2. The experiment was carried out in two stages, in early lactation as a randomized block design involving 18 Jersey cows fed to appetite and in mid-lactation as a 3 × 3 Latin square change-over design involving 12 cows, rationed according to milk yield.

3. There were no significant between-treatment differences in either milk yield or milk fat content in either stage of the experiment.

1. Large White x Landrace pigs were used to study the effects of supplementation with limiting amino acids of diets based on wheat containing 13% crude protein. Measurements were made of growth rate, feed conversion, carcass composition, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.

2. A wheat diet supplemented with lysine and threonine, the firstand the second-limiting amino acids respectively, produced almost the same growth rate and feed conversion ratio as one supplemented with fish meal and meat meal. Methionine was probably the thirdlimiting amino acid, and additional supplementation with methionine produced a further small improvement in growth rate and feed conversion ratio to the point where they were equal to those on the diet supplemented with fish meal and meat meal.

3. Supplementation of the wheat diet with lysine only produced the same growth rate and feed conversion ratio as a least-cost commercial diet; performance was, however, inferior to that on a wheat diet supplemented with fish meal and meat meal. The commercial diet had a lower dry-matter digestibility.

4. Eye-muscle area of pigs on the wheat diet supplemented with lysine was similar to that of pigs on a wheat diet supplemented with fish meal and meat meal; however, backfat thickness was significantly lower on the latter diet.

5. Except for threonine, plasma-free amino acid concentrations reflected with reasonable accuracy amino acid deficiencies in the diets.

A study of the British Friesian Cattle Society's herdbook for 1961 showed that twin births were registered from 323 cows which had borne single calves the year before, and which had 2009 contemporaries of the same age calving single births in the same two seasons and in the same herds.

Least squares means of milk yield and fat percentage calculated from the truncated 305-day lactation showed that the twin mothers exceeded their contemporaries by 118±47 kg milk in lactations 2 days shorter. After correction for herd and year effects there was no difference between the twin birth lactation yield and the preceding single birth yield.

There was a reduction in fat percentage of 0±06% associated with the twin birth lactation.

The proportion of a sample of 194 twin mothers failing to calve again was 24±3% against 19±1% of the mothers of single calves, but no reasons for culling had been recorded.

Twenty-seven groups of Finnish Landrace × Dorset Horn lambs each of 2 castrated males and 2 females were offered daily quantities of 180, 248 or 343 g of milk substitute dry matter (DM) for 21, 29 or 40 days. Concentrate pellets were available ad libitum and from 22 days of age 150 g of hay per week was offered. When the mean live weight of a group reached 35 kg two castrates and one female from each group were slaughtered and the carcasses appraised.

The growth rate and daily concentrate intake of lambs from 48 days of age until slaughter (reported -in this paper) were not affected by previous treatment, but lambs weaned at 40 days had a higher food conversion efficiency in this period (0·266 kg gain/kg feed DM) than those weaned at 21 days (0·244) or 29 days (0·232).

Delaying weaning from 21 to 29 and 40 days reduced overall concentrate DM intake from birth to slaughter (from 88·15 to 81·09 and 73·39 kg) but increased growth rate (261, 276 and 288 g/day) and the conversion of total DM consumed to live weight (0·300, 0·311 and 0·350 kg/kg). Increasing the daily allowance of milk substitute from 180 to 248 and 343 g/day also reduced total concentrate intake (84·18, 80·74 and 77·71 kg). Growth rate and food conversion efficiency tended to increase and concentrate DM intake to decrease when the same total quantity of milk substitute was given over a longer period. Castrated males grew faster than females (290 v. 260 g/day).

Weaning age generally had a greater effect than daily allowance of milk substitute on carcass measurements. Fat in the carcass tended to increase with increasing weaning age and significant interactions between daily allowance of milk substitute and weaning age were found for some carcass measurements.

In a series of feeding trials, measurements were made of silage drymatter (DM) content and pH, animal live weight and intake of DM other than silage. Silage intake has been related to these measurements by multiple regression. Subsequently, within the recorded ranges of the variables used, good predictions have been made of silage intake by large groups of cattle.

The carcass characteristics of young adult female pigs (gilts) slaughtered after weaning their first litters have been investigated using three groups of 19 Landrace × (Landrace×Large White) gilts. In two treatment groups gilts were mated at their pubertal oestrus and suckled their piglets for 5 to 11 and 35 to 42 days respectively. These gilts were slaughtered on average 10 days after weaning. A third control group consisted of unmated gilts slaughtered at 118 kg live weight.

There was no significant difference in the killing-out percentage for the three groups. The carcasses of the gilts which farrowed contained significantly less fat (P<0·001) than those of the unmated controls. The carcasses of the farrowed gilts had significantly lighter middle sections (P<0·001) and significantly heavier shoulders (P<0·001) than the controls.

Despite the variations in tissue yield and distribution, the yield of prime joints for the gilts which had farrowed was only 0·62 percentage units less than that of the controls.

No commercially significant variations between groups in meat quality were observed.

1. The effects of supplementing diets containing 10% or 17% crude protein wheat, vitamins and minerals with the limiting amino acids were studied with growing Large White x Landrace pigs. Performance was measured in terms of growth rate, feed conversion, carcass measurements, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.

2. With diets based on wheat containing 17% crude protein, a lysine supplement gave a slightly higher growth rate and a slightly lower feed conversion ratio than when fish meal and meat meal was the supplement.

3. With diets based on wheat containing 10% crude protein, performance was significantly poorer when the diet was supplemented with the four most limiting amino acids (lysine, threonine, valine, methionine) than with fish meal and meat meal. Meat meal and soya bean meal appeared to be a good source of the limiting amino acids, other than lysine, when added to a diet based on wheat containing 10% crude protein.

4. Eye-muscle area was lower and backfat thickness greater when diets based on wheat containing 10% crude protein were unsupplemented or supplemented with lysine than when they were supplemented with protein or with the four most limiting amino acids. However, no significant differences in backfat thickness were obtained between similar comparisons when the wheat contained 17% crude protein.

One hundred and twenty-eight Landrace and Large White pigs were allocated on the basis of sex, litter origin and initial weight to one of 16 treatments, made up of four basal 16, 18, 20 and 22% protein diets, each supplemented with either 0·00, 0·10, 0·15 or 0·20% synthetic DL-methionine, at a common digestible energy level of 3740 kcal/kg. Pigs were reared between 8 and 50 kg live weight. Growth rate of pigs and efficiency of feed conversion were significantly improved as the protein levels were increased up to the 20% protein level, optimal performance being on the 20% protein diet, with added 0·15% methionine, giving a total methionine+cystine level of 0·65% and a lysine level of 1·07%. Addition of synthetic methionine to the diets resulted in significant improvement in the rate and efficiency of gain only at the 16 and 18% protein levels.

Carcass leanness and fatness increased and decreased respectively over the whole range of protein levels. Graded addition of DL-methionine within each protein level did not influence carcass characteristics.

Nitrogen retention showed optimal utilization of dietary nitrogen to be at the 18% protein level, with a total dietary methionine + cystine level of 0·61%, which was at variance with the levels indicated by both growth and feed efficiency.